1. Field
One or more embodiments of the present disclosure relate to a cooling system and a superconducting magnet apparatus employing the same. More particularly, one or more embodiments of the present disclosure relate to a cooling system having an improved mounting structure of a cryocooler, and a superconducting magnet apparatus employing the cooling system.
2. Description of the Related Art
A superconducting apparatus, such as a magnet resonance imaging (MRI) apparatus or a nuclear magnetic resonance (NMR) apparatus, uses a superconducting magnet. Superconductivity is a phenomenon where zero electrical resistance and expulsion of magnetic fields occurs in certain materials when cooled below a characteristic critical temperature. Superconductivity is characterized by the Meissner effect, in which the complete ejection of magnetic field lines from the interior of the superconductor occurs as it transitions into the superconducting state. Since the superconducting magnet maintains a superconducting phenomenon at an extremely low temperature, such as 4.2 K (−452.11° F.), a cooling system is required to maintain such an extremely low temperature. A currently commercialized cooling system generally cools down a superconducting magnet by using liquid helium.
A two-stage cryocooler that is generally employed in a cooling system may include a first stage operating at a temperature ranging from 40 K to 50 K, and a second stage operating at a temperature of 4 K. The second stage cools down a superconductor by both direct and indirect thermal contact (i.e., a superconducting coil), and the first stage cools down via a thermal shield unit that suppresses heat transfer between a room temperature and the superconductor. In the two-stage cryocooler, the second stage is often directly placed into a helium space so as to directly contact and condense a helium gas.
In order to locate a second stage of a general cryocooler in a helium space, the general cryocooler is perpendicularly mounted on a chamber of a superconducting magnet apparatus. If the general cryocooler is not perpendicularly mounted on the chamber, a body of the general cryocooler needs to be in a vacuum space so as to prevent loss of helium. In this case, the second stage of the general cryocooler does not directly contact the helium steam, and thus, a thermal interface is required between the second stage and the helium steam. However, since the thermal conductivity of the thermal interface is limited, a cooling power of the general cryocooler deteriorates.